Threats from the inside of an organization’s perimeters are a significant problem, since it is difficult to distinguish them from benign activity. In this overview article we discuss defining properties of insiders and insider threats. After presenting definitions of these terms, we go on to discuss a number
of approaches from the technological, the sociological, and the socio-technical domain. We draw two main conclusions. Tackling insider threats requires a combination of techniques from the technical, the sociological, and the socio-technical domain, to enable qualified detection of threats, and their mitigation. Another important observation is that the distinction between insiders and outsiders seems to loose significance as IT infrastructure is used in performing insider attacks.